How does bone roll affect the rig importing into Unity game engine if it does at all?
Bone roll is important when using constraints, drivers, curves editing, clarity of animation programming; but after an animation is done and saved as Fbx, generally it's baked, so that a &quot;pure&quot; rig (a rig without constraints, drivers, control bones: made with deforming bones only) is exported.
This behaviour is set in the Fbx exporter preferences (bake animations, deforming bones only). The baked animation will correctly perform in Unity with any kind of bone roll.
Be aware that if you change the bone roll every previously made animation will be broken.
A common good practice is to set the &quot;main&quot; rotation of a bone as positive X axis.